The Long Term Evolution (LTE) wireless communication standard can offer a high-capacity, high-speed wireless interface for use by mobile phones, data terminals, machine-type-communication (MTC) or machine-to-machine (M2M) equipment, and similar devices. However, in some instances it may be desirable to sacrifice aspects of an LTE terminal's performance (such as its data capacity) in order to gain other benefits, such as a reduced complexity and/or cost. The 3rd Generation Partnership Project has considered such possibilities, for example in connection with “low-cost” or “limited capability” User Equipment (UE).
Release 13 of LTE proposed support for such a new Low Cost (LC) category of UE, sometimes referred to as “Category M”. Category M UEs have performance objectives of lower cost, low power consumption and enhanced coverage. The enhanced coverage capability that is defined may also be made available to other categories of UE. UEs which are in a poor coverage area may need to operate in a coverage enhancement mode in which messages need to be repeated a relatively large number of times on average in order to provide sufficient connectivity. Such devices may be targeted toward use cases requiring small amounts of data communication at relatively infrequent times, and may be suitable for M2M applications.
There is a need to define ways for an eNB to be able to contact these new types of UEs by paging them. For enhanced coverage cases, multiple repetitions of paging messages may be used when required to contact a UE.
A current implementation for Category M UEs for Release 13 of the LTE standard requires a UE to receive a Paging Radio Network Temporary Identifier (P-RNTI) with a correct Cyclic Redundancy Check (CRC) code. This P-RNTI is transmitted in a particular Physical Downlink Control Channel, denoted the M-PDCCH, and the P-RNTI content is not unique to a UE. The timing of the Paging Occasion (PO) containing a P-RNTI is specific to a UE by a calculation that includes the UE's identification. In current LTE implementations, pages are sent to UEs at known times in a PO within a paging frame. The UEs and the network calculate the paging frame and paging occasion within the frame based on a mutually known calculation that depends on both the UE identity, its UE_ID, which is its International Mobile Subscriber Identity (IMSI) and the DRX cycle for that UE. Details of this mechanism and calculation are in “LTE The UMTS Long Term Evolution”, 2nd Edition, Wiley, Edited by Stefania Sesia; p. 62 and p. 84-86. Extensions to the DRX time that can be configured to over 1 hour was proposed for release 13 of the LTE standard.
However, the above calculation can result in multiple UEs sharing a PO. Successful reception of P-RNTI corresponds to reception of a downlink grant that points to a Physical Downlink Shared Channel (PDSCH) where the actual page will be sent within the frequency band. In a proposed implementation of LTE Release 13, for UEs using coverage enhancement, the PDSCH containing the page is scheduled one or two subframes after the P-RNTI transmission or last repetition of the P-RNTI. The downlink grant indicates the timing. Only when the actual page is decoded will the UE be assured whether or not a page has been sent to it. The actual page will contain the IMSI of the targeted UE. The number of repetitions of the actual page can be the same as the number of P-RNTI repetitions.
If different numbers of possible repetitions of P-RNTI all ended at the same time, a UE attempting to receive them would potentially be required to combine all possible numbers of repetitions preceding that ending time. This would require extensive processing capability in order for all reception processes to complete in a sufficiently short time so as not to miss a potential paging message that could follow that P-RNTI. Thus one proposal is for the beginning of all possible combinations of repetitions of the P-RNTI to start at the same time, so that the endings will be at different times after that depending on the number of repetitions.
It is also possible that frequency hopping may be specified during P-RNTI repetition. Since Category M UEs can only receive 6 contiguous PRBs. The hopping would be to other blocks of 6 PRBs in systems containing sufficient bandwidth. This technique may reduce the required number of repetitions for a coverage level.
However, an unresolved issue is how an eNB can determine a level of coverage enhancement and therefore the number of repetitions that is needed to page a UE. Paging with too few repetitions results in a UE potentially failing to receive its page. Paging with too many repetitions represents a waste of communication resources. A further complication is that a UE may change its repetition needs, for example if the propagation environment changes and/or if the UE moves. In addition, the repetition level used by an eNB may not be known by a UE a priori, so the UE may be required to perform blind decoding on all possible repetition levels. Because repetition levels may be very long in the worst-case coverage scenarios, this represents a significantly time-consuming and power-consuming task for the UE. Because the algorithm used to determine which repetition level is used can be situational and implementation dependent, the UE may not be able to predict which repetition level will be used by the eNB, and hence the UE may have to assume the longest repetition level.
Therefore there is a need for a method and apparatus for paging terminals that is not subject to one or more limitations in the prior art.
This background information is provided for the purpose of making known information believed by the applicant to be of possible relevance to the present technology. No admission is necessarily intended, nor should be construed, that any of the preceding information constitutes prior art against the present technology.